The invention discloses a multi-user wireless communication system based on both-way trunk and a method thereof; the communication system comprises four multi-antenna transceivers (not only a transmitter but also a receiver) and a multi-antenna both-way trunk; each transceiver is composed of an orthogonal frequency division multiplexing (OFDM) modulator, an OFDM demodulator, a memory and a self-interference eliminator; the both-way trunk is composed of an OFDM modulator, an OFDM demodulator and a beam former and is a semi-duplex amplifying transmission relay. The communication method leads a complete communication process to be finished within two time slots; in the first time slot, the four transceivers send signals to the relay at the same time, and an orthogonal frequency division multiple access is adopted as a multiple access way; in the second time slot, the relay adopts orthogonal frequency division multiplexing / space division multiplexing multiple access (OFDM / SDMA) as a multiple access way for leading received signals after being processed to be broadcasted to the four transceivers. In the invention, two multiple access ways are integrated, and relay beam forming matrixes suitable for different requirements of relay antenna number are respectively designed by adopting the two methods, thereby effectively utilizing space diversity to eliminate interference among the transceivers, and compared with the existing relay communication technology, the higher system and speed are realized.